Method for controlling combustion air flow rate in continuous heating furnace, metal plate production method, and continuous heating furnace

Abstract

To provide a method for controlling combustion air flow rates in a continuous heating furnace enabling the adjustment of the optimum combustion air flow rates depending on the volume of fuel gas flow rates, a metal plate production method, and the continuous heating furnace.SOLUTION: A method for controlling combustion air flow rates in a continuous heating furnace, includes: a measurement step (step S1) of measuring oxygen concentrations in combustion zones 4, 5 of adjustment objects for each of the combustion zones 4, 5 of the adjustment objects, and measuring fuel gas flow rates and combustion air flow rates fed to burners B4, B5 installed at the combustion zones 4, 5 of the adjustment objects; a target oxygen concentration setting step (step S2) of setting target oxygen concentrations in the combustion zones 4, 5 of the adjustment objects based on the measured fuel gas flow rates to the burners B4, B5; and a combustion air flow rate adjustment step (step S3) of adjusting the combustion air flow rates fed to the burners B4, B5 so that the measured oxygen concentrations in the combustion zones 4, 5 of the adjustment objects reach the target oxygen concentrations.SELECTED DRAWING: Figure 5

Description

[Technical Field]

[0001] The present invention relates to a method for controlling the flow rate of combustion air in a continuous heating furnace, a method for manufacturing a metal plate, and a continuous heating furnace. [Background technology]

[0002] A continuous heating furnace has multiple combustion zones, divided into multiple zones along the transport direction of the material to be heated. The material is heated to the target heating temperature by being heated in each combustion zone in turn. Each combustion zone is equipped with a burner, and the heat treatment in each combustion zone is carried out by the burner.

[0003] In this continuous heating furnace, in order to maintain optimal combustion in the burners in each combustion zone, the fuel gas flow rate and combustion air flow rate supplied to the burners are controlled using the ratio of the fuel gas flow rate and combustion air flow rate to the burners.

[0004] In controlling the fuel gas flow rate and combustion air flow rate, lowering the ratio of the actual combustion air flow rate (air ratio) to the air flow rate (theoretical air amount) required for complete combustion of the fuel gas in the burner is advantageous for improving thermal efficiency and suppressing scale formation on the metal sheets being manufactured. Furthermore, considering fluctuations in the theoretical air amount of the fuel gas mixture (e.g., a mixture of blast furnace gas and coke oven gas) and the influence of air entering the furnace due to the opening and closing of the loading and unloading doors used to load and unload the slabs to be heated, it is preferable to measure the oxygen concentration in the furnace in each combustion zone and control combustion for each combustion zone based on the results of the oxygen concentration measurements.

[0005] As a conventional method for controlling the flow rate of combustion air, for example, a method for operating a continuous heating furnace as disclosed in Patent Document 1 is known. The method of operating a continuous heating furnace shown in Patent Document 1 involves arranging a combustion burner for localized heating at or near the entrance of the combustion zone located furthest downstream in the combustion exhaust gas flow among the combustion zones in the continuous heating furnace, and controlling the air ratio to the combustion burner so that the oxygen concentration in the combustion exhaust gas near the combustion burner becomes a target oxygen concentration.

[0006] This allows the heating furnace as a whole to be operated while maintaining a low air ratio without leaving unburned gas in the combustion exhaust gas. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Laid-Open No. 2001-272028 Summary of the Invention [Problem to be solved by the invention]

[0008] However, the conventional method of operating a continuous heating furnace shown in Patent Document 1 has the following problems.

[0009] That is, changes in the fuel gas flow rate change the distance between the oxygen analyzer in the furnace and the burner flame, the amount of outside air entering, etc., and change the measurement conditions for the oxygen concentration in the combustion exhaust gas in the furnace. However, in the method of operating a continuous heating furnace shown in Patent Document 1, the combustion air flow rate is controlled using the same preset target oxygen concentration regardless of the fuel gas flow rate, so depending on the fuel gas flow rate supplied to the combustion burner, there may be a shortage of combustion air, causing an increase in the concentration of unburned gas components, i.e., carbon monoxide, and posing a problem of combustion safety.

[0010] In addition, since complete combustion is not achieved, reducing unburned gas was an issue from the perspective of fuel consumption.

[0011] Therefore, the present invention has been made to solve these conventional problems, and its object is to provide a method for controlling the combustion air flow rate in a continuous heating furnace, a method for manufacturing a metal plate, and a continuous heating furnace, which enable optimal adjustment of the combustion air flow rate according to the fuel gas flow rate, thereby suppressing the generation of unburned gas and improving combustion safety and fuel consumption rate. [Means for solving the problem]

[0012] In order to solve the above-mentioned problems, one aspect of the present invention provides a method for controlling a combustion air flow rate in a continuous heating furnace, the method comprising: a furnace body having a plurality of combustion zones arranged along the transport direction of the material to be heated; and a plurality of burners installed in each of the plurality of combustion zones. The method controls the combustion air flow rate supplied to the burners installed in one or more combustion zones selected from the plurality of combustion zones as a target for adjustment. The method comprises the following steps: a measurement step for measuring the oxygen concentration in each combustion zone and measuring the fuel gas flow rate and combustion air flow rate supplied to the burners installed in the combustion zone; a target oxygen concentration setting step for setting a target oxygen concentration in the combustion zone based on the fuel gas flow rate to the burners in the combustion zone measured in the measurement step; and a combustion air flow rate adjustment step for adjusting the combustion air flow rate supplied to the burners in the combustion zone so that the oxygen concentration in the combustion zone measured in the measurement step becomes the target oxygen concentration set in the target oxygen concentration setting step.

[0013] In addition, another aspect of the present invention is a method for manufacturing a metal plate, which includes a heating step of heating the heated body, that is, a slab, in a continuous heating furnace in which the combustion air flow rate is controlled by the above-mentioned method for controlling the combustion air flow rate in a continuous heating furnace.

[0014] Another aspect of the present invention provides a continuous heating furnace comprising a furnace body having a plurality of combustion zones arranged along the transport direction of the material to be heated, and a plurality of burners installed in each of the plurality of combustion zones. For each combustion zone to be adjusted, which is one or more combustion zones selected from the plurality of combustion zones, the furnace comprises: an oxygen concentration meter that measures the oxygen concentration in the combustion zone to be adjusted; a fuel gas flow meter that measures the fuel gas flow rate supplied to the burner installed in the combustion zone to be adjusted; a combustion air flow meter that measures the combustion air flow rate supplied to the burner installed in the combustion zone to be adjusted; a target oxygen concentration setting unit that sets a target oxygen concentration in the combustion zone to be adjusted based on the fuel gas flow rate to the burner of the combustion zone to be adjusted measured by the fuel gas flow meter; and a combustion air flow rate adjustment unit that adjusts the combustion air flow rate supplied to the burner of the combustion zone to be adjusted so that the oxygen concentration in the combustion zone to be adjusted measured by the oxygen concentration meter becomes the target oxygen concentration set by the target oxygen concentration setting unit. [Effects of the Invention]

[0015] The method for controlling the combustion air flow rate in a continuous heating furnace, the method for manufacturing a metal plate, and the continuous heating furnace according to the present invention make it possible to optimally adjust the combustion air flow rate according to the magnitude of the fuel gas flow rate, thereby suppressing the generation of unburned gas and improving combustion safety and fuel consumption rate. [Brief explanation of the drawings]

[0016] [Figure 1] 1 is a schematic diagram of an example of a continuous heating furnace according to an embodiment of the present invention. FIG. [Figure 2] 1A and 1B are diagrams illustrating the control configuration of the combustion air flow rate supplied to the burners installed in the heating zone and the soaking zone, which are the combustion zones to be adjusted in the continuous heating furnace shown in FIG. 1 , where (a) is a diagram illustrating the control configuration of the combustion air flow rate supplied to the burners installed in the heating zone, and (b) is a diagram illustrating the control configuration of the combustion air flow rate supplied to the burners installed in the soaking zone. [Figure 3] FIG. 2 is an explanatory diagram for explaining an oxygen concentration meter. [Figure 4] FIG. 2 is a functional block diagram of a burner control device. [Figure 5] 10 is a flowchart illustrating a flow of control of the flow rate of combustion air supplied to burners installed in the heating zone and the soaking zone, which are combustion zones to be adjusted. [Figure 6] 10 is a graph showing a comparison between an example of the present invention and a comparative example regarding the relationship between the oxygen concentration in the soaking zone and the fuel gas flow rate. [Figure 7] 10 is a graph showing a comparison between an example of the present invention and a comparative example regarding the relationship between the carbon monoxide concentration in the soaking zone and the fuel gas flow rate. [Figure 8] 1 is a graph showing a comparison between an example of the present invention and a comparative example regarding the relationship between fuel consumption rate and efficiency. DETAILED DESCRIPTION OF THE INVENTION

[0017] Hereinafter, embodiments of the present invention will be described with reference to the drawings. The embodiments shown below are examples of devices and methods for embodying the technical concept of the present invention, and the technical concept of the present invention is not limited to the following embodiments in terms of the materials, shapes, structures, arrangements, etc. of the components.

[0018] In addition, the drawings are schematic, and therefore it should be noted that the relationship between thickness and planar dimensions, ratios, etc. may differ from the actual relationship, and the drawings may also contain parts where the relationship and ratio of dimensions differ from each other.

[0019] FIG. 1 shows an example of a continuous heating furnace according to an embodiment of the present invention. The continuous heating furnace 1 shown in FIG. 1 includes a furnace body 2 having multiple combustion zones arranged along the conveying direction (pass line, from left to right in FIG. 1) of a slab S as an object to be heated. The furnace body 2 is equipped with a charging door 6 for charging the slab S and an extraction door 7 for extracting the slab S after heating. In this embodiment, the multiple combustion zones are a preheating zone 3, a heating zone 4, and a soaking zone 5 arranged in this order from the charging side (upstream side) to the extraction side (downstream side). The example of the continuous heating furnace 1 shown in FIG. 1 illustrates a case where there is one heating zone 4 and one soaking zone 5, but two or more heating zones 4 and two or more soaking zones 5 may be provided.

[0020] A flue 8 is provided on the inlet side (upstream side) of the preheating zone 3. An air recuperator (air preheater) 9 and a gas recuperator (gas preheater) 10 are provided in the flue 8, and the tip of the flue 8 is connected to a chimney (not shown). In this embodiment, the two combustion zones, the heating zone 4 and the soaking zone 5, are the combustion zones to be adjusted.

[0021] A plurality of burners B3 (eight in this embodiment) are provided in the preheating zone 3. Of the plurality of burners B3, a predetermined number (four in this embodiment) of the burners B3 are installed at an upper position above the transport position of the slab S, and a predetermined number (four in this embodiment) of the burners B3 are installed at a lower position below the transport position of the slab S.

[0022] Then, the slab S is preheated in the preheating zone 3. When preheating the slab S, fuel gas and combustion air are supplied to each burner B3 at a flow rate that is a preset ratio in the preheating zone 3, and heating in the preheating zone 3 is performed.

[0023] Furthermore, a plurality of burners B4 (two in this embodiment) are provided in the heating zone 4, which is the combustion zone to be adjusted. Of the plurality of burners B4, a predetermined number (one in this embodiment) of burners B4 are installed at an upper position above the transport position of the slab S, and a predetermined number (one in this embodiment) of burners B4 are installed at a lower position below the transport position of the slab S.

[0024] Furthermore, a plurality of burners B5 (two in this embodiment) are provided in the soaking zone 5, which is the combustion zone to be adjusted. Of the plurality of burners B5, a predetermined number (one in this embodiment) of burners B5 are installed at an upper position above the transport position of the slab S, and a predetermined number (one in this embodiment) of burners B5 are installed at a lower position below the transport position of the slab S.

[0025] In the heating zone 4 and the soaking zone 5 other than the preheating zone 3, the flow rates of the fuel gas and combustion air supplied to the burners B4 and B5 are controlled using the ratio of the fuel gas flow rate and the combustion air flow rate supplied to the burners B4 and B5 to maintain optimal combustion of the slab S. The control of the combustion air flow rate supplied to the burners B4 and B5 is described below.

[0026] 1 and 2(a) and (b), the heating zone 4 and the soaking zone 5, which are the combustion zones to be adjusted, are each equipped with an oxygen concentration meter 11 that measures the oxygen concentration inside the heating zone 4 and the soaking zone 5, and a fuel gas flow meter 12 that measures the flow rate of fuel gas supplied to burners B4 and B5 installed in the heating zone 4 and the soaking zone 5, respectively. In addition, the heating zone 4 and the soaking zone 5 are each equipped with a combustion air flow meter 13 that measures the flow rate of combustion air supplied to burners B4 and B5 installed in the heating zone 4 and the soaking zone 5, respectively.

[0027] Furthermore, each fuel gas flow meter 12 is installed in a pipe that supplies fuel gas to each burner B4, B5, and the pipe is equipped with a fuel gas flow control valve 14. Furthermore, each combustion air flow meter 13 is installed in a pipe that supplies combustion air to each burner B4, B5, and the pipe is equipped with a combustion air flow control valve 15.

[0028] Each oxygen concentration meter 11, each fuel gas flow meter 12, each combustion air flow meter 13, and each combustion air flow control valve 15 are connected to burner control devices BC4 and BC5, which control the combustion air flow rate supplied to burners B4 and B5.

[0029] Here, each oxygen concentration meter 11 is a sensor that measures the oxygen concentration inside the heating zone 4 and the soaking zone 5, respectively. Each of the oxygen concentration meters 11 is preferably a laser gas analyzer capable of measuring the oxygen concentration at a plurality of locations within the heating zone 4 and the soaking zone 5 .

[0030] As shown in FIG. 3, the laser gas analyzer constituting the oxygen concentration meter 11 includes a light emitter 11a that emits laser light and a light receiver 11b that receives the laser light. The light emitter 11a is installed on one widthwise side of each of the heating zone 4 and the soaking zone 5, and the light receiver 11b is installed on the other widthwise side of each of the heating zone 4 and the soaking zone 5 so as to face the light emitter 11a. This makes it possible to measure the average oxygen concentration at multiple locations in the widthwise direction of each of the heating zone 4 and the soaking zone 5. By irradiating the laser light in the widthwise direction of each of the heating zone 4 and the soaking zone 5 in this way, interference of the laser light with the slab S during transportation can be suppressed compared to a configuration in which the laser light is irradiated in the vertical direction, thereby improving the accuracy of oxygen concentration measurement.

[0031] The installation positions of each oxygen concentration meter 11 in the heating zone 4 and the soaking zone 5 are preferably near the center in the height direction of each of the heating zone 4 and the soaking zone 5 (around above the slab S), because measurement accuracy deteriorates when the flames of burners B4 and B5 hit the oxygen concentration meter 11. In the heating zone 4, the oxygen concentration meter 11 is preferably installed on the preheating zone 3 side (upstream side) to efficiently measure the concentration of the gas flowing from the preheating zone 3. In the soaking zone 5, the gas concentration changes drastically near the extraction door 7 (downstream side), so the oxygen concentration meter 11 is preferably installed on the heating zone 4 side (upstream side) where the concentration is stable.

[0032] Furthermore, each fuel gas flow meter 12 measures the flow rate of fuel gas in the pipes that supply the fuel gas to each burner B4, B5. Each combustion air flow meter 13 measures the flow rate of combustion air in the pipes that supply the combustion air to each burner B4, B5.

[0033] Furthermore, each fuel gas flow rate adjustment valve 14 adjusts the flow rate of fuel gas in the pipes that supply fuel gas to each burner B4, B5. Furthermore, each combustion air flow rate adjustment valve 15 adjusts the flow rate of combustion air in the pipes that supply combustion air to each burner B4, B5.

[0034] Furthermore, burner control devices BC4 and BC5 control the combustion air flow rates supplied to burners B4 and B5, respectively. It is not necessary to provide two burner control devices BC4 and BC5; one burner control device may control the combustion air flow rates supplied to burners B4 and B5. Also, some of the processing performed by each burner control device BC4 and BC5 may be performed by a common processing unit.

[0035] 2(a) and 2(b), fuel gas flow meter 12, combustion air flow meter 13, fuel gas flow control valve 14, and combustion air flow control valve 15 are connected only to upper burners B4 and B5, and burner control devices BC4 and BC5 are shown as only controlling the combustion air flow rate supplied to the upper burners 4 and 5. However, although not shown, separate fuel gas flow meter 12, combustion air flow meter 13, fuel gas flow control valve 14, and combustion air flow control valve 15 are also connected to lower burners B4 and B5, and separate lower burner control devices BC4 and BC5 control the combustion air flow rate supplied to the lower burners 4 and 5. One oxygen concentration meter 11 is installed in each of heating zone 4 and soaking zone 5, and this oxygen concentration meter 11 is connected not only to upper burner control devices BC4 and BC5 but also to lower burner control devices BC4 and BC5.

[0036] Each of the burner control devices BC4 and BC5 is a computer system equipped with an arithmetic processing device. As shown in Fig. 4, each of the burner control devices BC4 and BC5 has, as functional blocks, a measurement data input unit 21, a target oxygen concentration setting unit 22, and a combustion air flow rate adjustment unit 23. Each of the burner control devices BC4 and BC5 executes the measurement data input function of the measurement data input unit 21, the target oxygen concentration setting function of the target oxygen concentration setting unit 22, and the combustion air flow rate adjustment function of the combustion air flow rate adjustment unit 23 in accordance with instructions from an installed program.

[0037] Measurement data of the oxygen concentration inside each of the heating zone 4 and the soaking zone 5, measured by oxygen concentration meters 11 provided in each of the heating zone 4 and the soaking zone 5, is input to the measurement data input unit 21 of each of the burner control devices BC4 and BC5. In addition, measurement data of the fuel gas flow rate supplied to each of the burners B4 and B5, measured by fuel gas flow meters 12 provided in the pipes supplying fuel gas to each of the burners B4 and B5, and measurement data of the combustion air flow rate supplied to each of the burners B4 and B5, measured by combustion air flow meters 13 provided in the pipes supplying combustion air to each of the burners B4 and B5, are input to the measurement data input unit 21 of each of the burner control devices BC4 and BC5 at a preset sampling period.

[0038] The target oxygen concentration setting unit 22 of each of the burner control devices BC4 and BC5 sets the target oxygen concentration within each of the heating zone 4 and the soaking zone 5 based on the measurement data of the fuel gas flow rate to each of the burners B4 and B5 input into the measurement data input unit 21 of each of the burner control devices BC4 and BC5.

[0039] When setting this target oxygen concentration, an oxygen concentration target value determined in advance for each fuel gas flow rate is used. The oxygen concentration target values ​​determined in advance for each fuel gas flow rate are stored in the target oxygen concentration setting unit 22 of each burner control device BC4, BC5. For example, in this embodiment, for fuel gas flow rates A1 to A2, X1 is set as the oxygen concentration target value. Because conditions such as the amount of outside air entering the heating zone 4 and the soaking zone 5 as the combustion zones to be adjusted differ, it is desirable to determine an oxygen concentration target value appropriate for each of the heating zone 4 and the soaking zone 5 as the combustion zones to be adjusted.

[0040] Furthermore, the combustion air flow rate adjusting unit 23 of each of the burner control devices BC4 and BC5 adjusts the combustion air flow rate supplied to the burners B4 and B5 installed in the heating zone 4 and the soaking zone 5, respectively, as the combustion zones to be adjusted, so that the oxygen concentrations inside the heating zone 4 and the soaking zone 5, respectively, inputted into the measurement data input unit 21 of each of the burner control devices BC4 and BC5, become the target oxygen concentrations inside the heating zone 4 and the soaking zone 5, respectively, set by the target oxygen concentration setting unit 22 of each of the burner control devices BC4 and BC5.

[0041] Specifically, combustion air flow rate adjustment unit 23 of each burner control device BC4, BC5 calculates the combustion air flow rate to be supplied to burners B4, B5 such that the oxygen concentrations inside heating zone 4 and soaking zone 5, respectively, input to measurement data input unit 21 of each burner control device BC4, BC5, become the target oxygen concentrations inside heating zone 4 and soaking zone 5, respectively, set by target oxygen concentration setting unit 22 of each burner control device BC4, BC5. Then, the difference between the measurement data of the combustion air flow rate to be supplied to burners B4, B5 input to measurement data input unit 21 of each burner control device BC4, BC5 and the calculated combustion air flow rate to be supplied to burners B4, B5 is calculated, and the valve opening of each combustion air flow rate adjustment valve 15 of each burner B4, B5 is adjusted to eliminate the difference.

[0042] In this manner, the flow rate of combustion air supplied to each of the burners B4 and B5 is controlled. Next, with reference to FIG. 5, a flow of control of the flow rate of combustion air supplied to burners B4 and B5 installed in heating zone 4 and soaking zone 5, respectively, as combustion zones to be adjusted, will be described.

[0043] When controlling the flow rate of combustion air supplied to burners B4 and B5 installed in the heating zone 4 and the soaking zone 5, which are the combustion zones to be adjusted, respectively, steps S1 to S3 shown in FIG. 5 are performed for each of the heating zone 4 and the soaking zone 5, which are the combustion zones to be adjusted.

[0044] First, in step S1, oxygen concentration meters 11 installed in the heating zone 4 and the soaking zone 5 measure the oxygen concentration inside each of the heating zone 4 and the soaking zone 5. In addition, a fuel gas flow meter 12 installed in the piping that supplies fuel gas to each burner B4, B5, installed in the heating zone 4 and the soaking zone 5, measures the flow rate of fuel gas supplied to each burner B4, B5. In addition, a combustion air flow meter 13 installed in the piping that supplies combustion air to each burner B4, B5, installed in the heating zone 4 and the soaking zone 5, measures the flow rate of combustion air supplied to each burner B4, B5 (measurement step).

[0045] Next, in step S2, the burner control devices BC4 and BC5 each set a target oxygen concentration within the heating zone 4 and the soaking zone 5 based on the fuel gas flow rates to the burners B4 and B5 in the heating zone 4 and the soaking zone 5 measured in step S1 (measurement process) (target oxygen concentration setting process).

[0046] Specifically, measurement data of the oxygen concentration inside each of the heating zone 4 and the soaking zone 5 measured in step S1 (measurement process) is input to measurement data input units 21 of each of the burner control devices BC4 and BC5. Also input to the measurement data input units 21 are measurement data of the fuel gas flow rate supplied to each of the burners B4 and B5 measured in step S1 (measurement process) and measurement data of the combustion air flow rate supplied to each of the burners B4 and B5 measured in step S1 (measurement process).

[0047] Then, the target oxygen concentration setting unit 22 of each of the burner control devices BC4 and BC5 sets the target oxygen concentration within each of the heating zone 4 and the soaking zone 5 based on the measurement data of the fuel gas flow rate to the burners B4 and B5 inputted to the measurement data input unit 21 of each of the burner control devices BC4 and BC5.

[0048] When setting this target oxygen concentration, as described above, an oxygen concentration target value determined in advance for each fuel gas flow rate is used. The oxygen concentration target values ​​determined in advance for each fuel gas flow rate are stored in the target oxygen concentration setting units 22 of the burner control devices BC4 and BC5. For example, in this embodiment, for fuel gas flow rates A1 to A2, X1 is set as the oxygen concentration target value. Because conditions such as the amount of outside air entering the heating zone 4 and the soaking zone 5 as the combustion zones to be adjusted differ, it is desirable to determine an oxygen concentration target value appropriate for each of the heating zone 4 and the soaking zone 5 as the combustion zones to be adjusted.

[0049] Next, in step S3, the burner control devices BC4 and BC5 each adjust the combustion air flow rate supplied to the burners B4 and B5 in the heating zone 4 and the soaking zone 5, respectively, so that the oxygen concentration inside the heating zone 4 and the soaking zone 5, respectively, measured in step S1 (measurement process) becomes the target oxygen concentration set in step S2 (target oxygen concentration setting process) (combustion air flow rate adjustment process).

[0050] Specifically, as described above, the combustion air flow rate adjuster 23 of each of the burner control devices BC4 and BC5 calculates the combustion air flow rate to be supplied to burners B4 and B5 such that the oxygen concentrations inside the heating zone 4 and the soaking zone 5, measured in step S1 (measurement step) and input to the measurement data input unit 21 of each of the burner control devices BC4 and BC5, become the target oxygen concentrations inside the heating zone 4 and the soaking zone 5, respectively, set in step S2 (target oxygen concentration setting step).The difference between the measurement data of the combustion air flow rates supplied to burners B4 and B5 in the heating zone 4 and the soaking zone 5, input to the measurement data input unit 21 of each of the burner control devices BC4 and BC5, and the calculated combustion air flow rates to be supplied to burners B4 and B5 in the heating zone 4 and the soaking zone 5, is then calculated, and the valve aperture of each combustion air flow rate adjuster valve 15 of each burner B4 and B5 is adjusted to eliminate the difference.

[0051] This completes the control of the flow rate of combustion air supplied to the burners B4 and B5 installed in the heating zone 4 and the soaking zone 5, respectively, as the combustion zones to be adjusted. As described above, according to the method for controlling the combustion air flow rate in a continuous heating furnace of this embodiment, the combustion air flow rate supplied to burners B4 and B5 installed in heating zone 4 and soaking zone 5, respectively, as combustion zones to be adjusted, which are one or more combustion zones selected from the plurality of combustion zones 3, 4, and 5, is controlled by performing a measurement step (step S1), a target oxygen concentration setting step (step S2), and a combustion air flow rate adjustment step (step S3) for each heating zone 4 and soaking zone 5 as combustion zones to be adjusted.

[0052] In the measurement process (step S1), the oxygen concentration inside each of the heating zone 4 and the soaking zone 5 is measured, and the fuel gas flow rate and combustion air flow rate supplied to the burners B4 and B5 installed in the heating zone 4 and the soaking zone 5, respectively, are measured.

[0053] In addition, in the target oxygen concentration setting process (step S2), the target oxygen concentrations in the heating zone 4 and the soaking zone 5 are set based on the fuel gas flow rates to the burners B4 and B5 of the heating zone 4 and the soaking zone 5, respectively, measured in the measurement process (step S1).

[0054] Furthermore, in the combustion air flow rate adjustment process (step S3), the combustion air flow rates supplied to the burners B4 and B5 in the heating zone 4 and the soaking zone 5, respectively, are adjusted so that the oxygen concentrations inside the heating zone 4 and the soaking zone 5 measured in the measurement process (step S1) become the target oxygen concentrations set in the target oxygen concentration setting process (step S2).

[0055] This allows the generation of unburned gas to be suppressed and combustion safety and fuel consumption rate to be improved by setting a target oxygen concentration appropriate for each fuel gas flow rate, taking into consideration fluctuations in the distance between the oxygen analyzer and the burner flame due to the magnitude of the fuel gas flow rate, fluctuations in the amount of outside air entering, and controlling the combustion air flow rate to achieve the target oxygen concentration in accordance with fluctuations in the fuel gas flow rate.In other words, it is possible to adjust the combustion air flow rate to an optimum level in accordance with the magnitude of the fuel gas flow rate, suppress the generation of unburned gas, and improve combustion safety and fuel consumption rate.

[0056] Furthermore, according to the method for controlling the combustion air flow rate in a continuous heating furnace according to this embodiment, the multiple combustion zones 3, 4, and 5 in the continuous heating furnace 1 are composed of a preheating zone 3, one or more heating zones 4, and one or more soaking zones 5, which are arranged in this order from the charging side of the slab S as the object to be heated to the extraction side. The combustion zones to be adjusted are both the heating zone 4 and the soaking zone 5.

[0057] As a result, both the heating zone 4 and the soaking zone 5, which are most susceptible to the effects of fluctuations in the distance between the oxygen analyzer and the burner flame due to the magnitude of the fuel gas flow rate and fluctuations in the amount of outside air entering, are treated as combustion zones to be adjusted, and it is possible to adjust the combustion air flow rate optimally in both the heating zone 4 and the soaking zone 5 according to the magnitude of the fuel gas flow rate, thereby suppressing the generation of unburned gas and improving combustion safety and fuel consumption rate.

[0058] Furthermore, according to the method for controlling the combustion air flow rate in a continuous heating furnace according to this embodiment, the oxygen concentration measured in each of the heating zone 4 and the soaking zone 5 in the measurement step (step S1) is the average value of the measured values ​​at multiple points in each of the heating zone 4 and the soaking zone 5. This makes it possible to appropriately measure the oxygen concentration inside each of the heating zone 4 and the soaking zone 5, which are the combustion zones to be adjusted.

[0059] Furthermore, according to the method for controlling the combustion air flow rate in a continuous heating furnace according to this embodiment, the measurement of the oxygen concentration inside each of the heating zone 4 and the soaking zone 5 in the measurement step (step S1) is performed using a laser gas analyzer.

[0060] This makes it possible to measure the average value of the oxygen concentration at multiple locations in the width direction of each of the heating zone 4 and the soaking zone 5. By irradiating laser light in the width direction of each of the heating zone 4 and the soaking zone 5 using a laser gas analyzer, it is possible to suppress interference of the laser light with the slab S during transportation compared to a configuration in which laser light is irradiated in the vertical direction, and it is possible to improve the accuracy of the oxygen concentration measurement.

[0061] In addition, the metal plate manufacturing method of this embodiment includes a heating step of heating a slab S, which is the object to be heated, using a continuous heating furnace 1 in which the combustion air flow rate is controlled using the method for controlling the combustion air flow rate in the continuous heating furnace described above.

[0062] Furthermore, the continuous heating furnace 1 according to this embodiment is equipped with an oxygen concentration meter 11 for measuring the oxygen concentration inside each of the heating zones 4 and the soaking zones 5, which are combustion zones to be adjusted and which are one or more combustion zones selected from the plurality of combustion zones, a fuel gas flow meter 12 for measuring the fuel gas flow rate supplied to burners B4 and B5 installed in each of the heating zones 4 and the soaking zones 5, and a combustion air flow meter 13 for measuring the combustion air flow rate supplied to burners B4 and B5 installed in each of the heating zones 4 and the soaking zones 5. Furthermore, for each of the heating zone 4 and the soaking zone 5, a target oxygen concentration setting unit 22 is provided which sets a target oxygen concentration within each of the heating zone 4 and the soaking zone 5 based on the fuel gas flow rate to the burners B4 and B5 of each of the heating zone 4 and the soaking zone 5 measured by the fuel gas flow meter 12, and a combustion air flow rate adjustment unit 23 is provided which adjusts the flow rate of combustion air supplied to the burners B4 and B5 of each of the heating zone 4 and the soaking zone 5 so that the oxygen concentration within each of the heating zone 4 and the soaking zone 5 measured by the oxygen concentration meter 11 becomes the target oxygen concentration set by the target oxygen concentration setting unit 22.

[0063] This allows the generation of unburned gas to be suppressed, and combustion safety and fuel consumption rate to be improved by taking into account fluctuations in the distance between the oxygen concentration meter and the burner flame due to the magnitude of the fuel gas flow rate, fluctuations in the amount of outside air entering, etc., and setting a target oxygen concentration appropriate for each fuel gas flow rate, and controlling the combustion air flow rate so that the target oxygen concentration is achieved in accordance with fluctuations in the fuel gas flow rate.

[0064] Although the embodiment of the present invention has been described above, the present invention is not limited to this and various modifications and improvements can be made.

[0065] For example, although two combustion zones, the heating zone 4 and the soaking zone 5, are set as combustion zones to be adjusted, only the heating zone 4 or only the soaking zone 5 may be set as combustion zones to be adjusted. Also, the preheating zone 3 may be set as combustion zone to be adjusted. [Example]

[0066] In order to verify the effects of the present invention, the relationship between the oxygen concentration in the soaking zone and the fuel gas flow rate, and the relationship between the carbon monoxide concentration in the soaking zone and the fuel gas flow rate were investigated for the present invention example and the comparative example.

[0067] In the present invention, the following steps were carried out in the soaking zone 5: a measurement step in which the oxygen concentration in the soaking zone 5 was measured, and the fuel gas flow rate and combustion air flow rate supplied to burner B5 installed in the soaking zone 5 were measured; a target oxygen concentration setting step in which a target oxygen concentration in the soaking zone 5 was set based on the fuel gas flow rate to burner B5 in the soaking zone 5 measured in the measurement step; and a combustion air flow rate adjustment step in which the combustion air flow rate supplied to burner B5 in the soaking zone 5 was adjusted so that the oxygen concentration in the soaking zone 5 measured in the measurement step became the target oxygen concentration set in the target oxygen concentration setting step.

[0068] In contrast, in the comparative example, the target oxygen concentration in the soaking zone 5 was set to a constant value, and the flow rate of combustion air supplied to burner B5 in the soaking zone 5 was adjusted so that the measured oxygen concentration in the soaking zone 5 would become the target oxygen concentration of the constant value.

[0069] In the comparative example, as shown in Figure 6, the target oxygen concentration in the soaking zone 5 was set to a constant value regardless of the fuel gas flow rate, so the oxygen concentration was generally uniform across the fuel gas flow rate ranges. However, when the fuel gas flow rate is low, outside air is more likely to enter the continuous heating furnace 1 than when the fuel gas flow rate is high, which increases the oxygen concentration. Furthermore, when the fuel gas flow rate is low, the distance between the burner B5 flame and the oxygen concentration meter 11 is greater, making it difficult to measure the gas components and leading to a high oxygen concentration. Therefore, in the comparative example, the combustion air flow rate was controlled to an extremely low level, which increased the concentration of unburned gas components, i.e., carbon monoxide, in the low fuel gas flow range, as shown in Figure 7, potentially resulting in an explosion or carbon monoxide leakage outside the furnace. Furthermore, if the target oxygen concentration were to be uniformly increased not only in the low flow rate range but also in the high flow rate range, this would result in a deterioration in fuel consumption and increased scale formation in the high flow rate range.

[0070] In contrast, in the case of the present invention, as shown in Figure 6, the target oxygen concentration is set higher only in the low flow rate region of fuel gas, which is a safety issue, and as shown in Figure 7, the carbon monoxide concentration can be reduced only in the low flow rate region of fuel gas, making it possible to optimally control the combustion air flow rate according to the magnitude of the fuel gas flow rate. FIG. 8 shows a comparison of the relationship between fuel consumption rate and efficiency between the example of the present invention and the comparative example.

[0071] In the case of the example of the present invention, the reduction in unburned gas enabled an improvement in fuel consumption rate (comparative example: 280.0 Mcal / t → example of the present invention: 276.6 Mcal / t). [Explanation of symbols]

[0072] 1. Continuous heating furnace 2 Furnace body 3 Preheat zone (burning zone) 4. Heating zone (combustion zone to be adjusted) 5. Equalizing zone (combustion zone to be adjusted) 6 Loading door 7 Extraction door 8 flue 9 Air Recuperator 10 Gas recuperator 11 Oxygen concentration meter 11a Light-emitting organ 11b Receiver 12 Fuel gas flow meter 13 Combustion air flow meter 14 Fuel gas flow control valve 15 Combustion air flow control valve 21 Measurement data input section 22 Target oxygen concentration setting unit 23 Combustion air flow rate adjustment unit B3 Burner B4 Burner B5 Burner BC4 Burner Control Device BC5 Burner Control Device S slab (heated object)

Claims

1. A method for controlling a combustion air flow rate in a continuous heating furnace having a furnace body with a plurality of combustion zones arranged along a transport direction of a heated material, and a plurality of burners installed in each of the plurality of combustion zones, comprising: Regarding the control of the flow rate of combustion air supplied to a burner installed in a combustion zone to be adjusted, which is one or more combustion zones selected from the plurality of combustion zones, For each combustion zone to be adjusted, a measuring step of measuring the oxygen concentration in the combustion zone to be adjusted and measuring the fuel gas flow rate and the combustion air flow rate supplied to a burner installed in the combustion zone to be adjusted; a target oxygen concentration setting step of setting a target oxygen concentration in the combustion zone to be adjusted based on the fuel gas flow rate to the burner in the combustion zone to be adjusted measured in the measurement step; a combustion air flow rate adjusting step of adjusting the combustion air flow rate supplied to a burner in the combustion zone to be adjusted so that the oxygen concentration in the combustion zone to be adjusted measured in the measuring step becomes the target oxygen concentration set in the target oxygen concentration setting step; A method for controlling the flow rate of combustion air in a continuous heating furnace, characterized by carrying out the following.

2. the plurality of combustion zones are composed of a preheating zone, one or more heating zones, and one or more soaking zones, which are arranged in this order from the charging side of the heated material to the extraction side, 2. The method for controlling a combustion air flow rate in a continuous heating furnace according to claim 1, wherein the combustion zone to be adjusted is at least one of the preheating zone and the soaking zone.

3. 3. The method for controlling a combustion air flow rate in a continuous heating furnace according to claim 1, wherein the oxygen concentration in the combustion zone to be adjusted measured in the measurement step is an average value of measured values ​​at a plurality of locations in the combustion zone to be adjusted.

4. 4. The method for controlling a combustion air flow rate in a continuous heating furnace according to claim 3, wherein the measurement of the oxygen concentration in the combustion zone to be adjusted in the measurement step is carried out using a laser gas analyzer.

5. 3. A method for manufacturing a metal plate, comprising a heating step of heating a slab, which is the object to be heated, in a continuous heating furnace in which the combustion air flow rate is controlled by the method for controlling the combustion air flow rate in a continuous heating furnace according to claim 1 or 2.

6. A continuous heating furnace comprising a furnace body having a plurality of combustion zones arranged along the transport direction of the heated material, and a plurality of burners installed in each of the plurality of combustion zones, Regarding the combustion zone to be adjusted, which is one or more combustion zones selected from the plurality of combustion zones, For each combustion zone to be adjusted, an oxygen concentration meter for measuring the oxygen concentration in the combustion zone to be adjusted; a fuel gas flow meter for measuring a flow rate of fuel gas supplied to a burner installed in the combustion zone to be adjusted; a combustion air flow meter for measuring a flow rate of combustion air supplied to a burner installed in the combustion zone to be adjusted; a target oxygen concentration setting unit that sets a target oxygen concentration in the combustion zone to be adjusted based on the fuel gas flow rate to a burner in the combustion zone to be adjusted measured by the fuel gas flow meter; a combustion air flow rate adjusting unit that adjusts the flow rate of combustion air supplied to a burner in the combustion zone to be adjusted so that the oxygen concentration in the combustion zone to be adjusted measured by the oxygen concentration meter becomes the target oxygen concentration set by the target oxygen concentration setting unit; A continuous heating furnace comprising:

7. 7. The continuous heating furnace according to claim 6, wherein the oxygen concentration meter is a laser gas analyzer.

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